The disclosure relates in general to a flat panel display, and more particularly, to a flat panel display, which uses a gate driving device manufactured by an amorphous silicon manufacturing process and can eliminate a residual image after the display is turned off.
In the typical LCD architecture, a residual image is frequently seen on the display, e.g., a LCD panel, after the LCD panel is turned off and the residual image cannot disappear until several seconds have elapsed. This phenomenon interferes with the visual feeling of the user, and the display quality of the LCD panel is deteriorated with time. Taking a thin-film transistor (TFT) LCD as an example, one of the reasons causing the residual image to occur after the LCD is turned off is that the discharging speed of the pixel electrodes of the TFT-LCD is too slow. Thus, the charges cannot be quickly released and remain in the liquid crystal capacitors after the LCD is turned off, and cannot be completely discharged until a period of time has elapsed.
FIG. 1 (Prior Art) is a schematic illustration showing a conventional LCD 10. In the LCD 10, a timing controller (not depicted in FIG. 1) outputs data, wherein a source driver of a display array circuit is utilized to receive and write the data, and gate drivers 12y (y=1 to P, and P is a positive integer) are utilized to select a row for writing the data so that an output frame is displayed on a panel 16. Then, when the LCD is turned off, a voltage detecting circuit 142 of a printed circuit board 14 detects that a received operation voltage VCC is lowered to a predetermined level (e.g., 0.7VCC), an off-controlling signal XAO is transformed from a high-level voltage H to a low-level voltage L and then outputted to the gate drivers 12y (y=1 to P). Thus, an output signal of each of the gate drivers 12y (y=1 to P) is transformed into the high-level voltage H to turn on TFTs of each pixel in the panel 16. FIG. 2 (Prior Art) shows signal waveforms in the LCD 10 of FIG. 1. Consequently, before the LCD is powered off, residual charges in a liquid crystal capacitor of each pixel can be rapidly discharged by the turned-on TFT and a data line electrically connected thereto. Thus, the time of completely discharging the residual charges can be shortened, thereby eliminating the phenomenon of the residual image when the LCD is turned off.
However, the property of the TFT-LCD is that a light source mainly comes from a backside, and a glass substrate has to be used. Thus, when the application field is an active mode LCD, transistors serving as switches have to be formed on the glass substrate using the semiconductor manufacturing process. However, the melting point of the glass is about 660°C., and the glass substrate cannot be used in the frequently used IC manufacturing process, such as the monocrystalline silicon manufacturing process (the growing temperature is higher than 1000° C.). In order to overcome this drawback, an amorphous silicon (Amorphous Si) manufacturing process, in which the amorphous silicon can be easily deposited on a large area and can be well attached to the glass substrate, is frequently used. FIG. 3 is a block diagram showing an amorphous silicon gate driver. As shown in FIG. 3, an amorphous silicon gate driver 300 has many shift registers 31n (n=1 to (N+1)).
FIG. 4 is a circuit diagram showing a shift register 31n of FIG. 3, wherein n is a positive integer ranging from 1 to (N+1). As shown in FIG. 3 and FIG. 4 and compared with the gate drivers 12y (y=1 to P) of FIG. 1, the amorphous silicon gate driver 300 does not have the function of an off-controlling signal XAO (i.e., does not have the function of eliminating the residual image after the LCD is turned off). This is because the off-controlling signal XAO is a low-level voltage (about 0 to 3.3 volts) in the conventional LCD 10 and can be received by the shift register (not depicted in the drawing) in the gate drivers 12y (y=1 to P). In the amorphous silicon manufacturing process, however, the off-controlling signal XAO is a high-level voltage, which may reach as high as 20 volts, and cannot be received by the shift registers 31x (x=1 to (N+1)). So, the problem of the residual image after the LCD is turned off appears again if a gate driving device of the LCD is manufactured by the amorphous silicon manufacturing process.
There is a need for a flat panel display, which can use a gate driving device manufactured by an amorphous silicon manufacturing process and can make all pixel electrodes discharge according to an off-controlling signal to eliminate a residual image when the flat panel display is turned off.